1. Technical Field
Example embodiments relate to a communication system, for example, to a receiver and a communication system having the same.
2. Description of the Related Art
Communication systems typically include a transmitter and a receiver. Data transmission methods of the communication systems are divided into a synchronous transmission method, a mesochronous transmission method, and a plesiochronous transmission method according to clock signals used for sampling data in the receiver.
In the communication system using the synchronous transmission method, a frequency and a phase of a clock signal used in a receiver are substantially the same as a frequency and a phase of a clock signal used in a transmitter. In the communication system using the mesochronous transmission method, the frequencies of the clock signals used in the receiver and the transmitter are identical to each other. However, the phases of the clock signals used in the receiver and the transmitter in the communication system using the mesochronous transmission method are different from each other. In the communication system using the plesiochronous transmission method, the frequency and the phase of the clock signal used in the receiver are different from the frequency and the phase of the clock signal used in the transmitter.
Therefore, the receiver in the communication system using the plesiochronous transmission method needs to have a clock and data recovery circuit (CDR) for recovering clock and data.
When the frequencies of clock signals used for the receiver and the transmitter are different from each other, an edge of the clock signal of the transmitter continually moves toward one direction on the basis of the clock signal of the transmitter, and then a sinusoidal jitter in the CDR may occur. The sinusoidal jitter may increase according to an increase of the transmission frequency.
The sinusoidal jitter caused by frequency difference between the clock signals of the receiver and the transmitter degrades performance of the CDR and increases a bit error rate (BER). Therefore, a means for adjusting the frequency of the clock signal is required such that the frequency of the clock signal of the receiver is substantially identical to the frequency of the clock signal of the transmitter.